Heat flux through wall question

In summary, the problem involves calculating the heat flux through a wall made of face brick, concrete block, and an air cavity, with given interior and exterior convection coefficients, thermal conductivities, and temperatures. The solution requires using the Rtotal equation and the heat transfer rate equation, but the lack of dimensions for the wall may make it difficult to calculate the area. One solution could be to assume a unit area of 1 m2 for the wall.
  • #1
Physicsswag
2
0

Homework Statement



I was given this question.

The wall of a building is constructed of face brick (10cm thick) and concrete block (50 cm thick) with an air filled cavity (5cm thick). The interior and exterior convection coefficients are 8.3 W.m^-2.K^_1 and 35W.m^-2.K^_1 respectively. The brick thermal conductivity is 0.79W.m^-1.K^_1 , the concrete block 1.63W.m^-1.K^_1, and the air cavity 0.26W.m^-1.K^_1. If the ambient air temperature is -10 degrees celsius and the room air temperature is 21 degrees Celsius, what will be the Heat flux through the wall.

Homework Equations


I know that Rtotal is equal to 1/h-inA + L1/k1A + ... + Ln/knA + 1/h-outA (h= Heat transfer coefficient, k= thermal conductivity, L=length, A=area)

Heat transfer rate = (t1-t2)/Rtotal

Heat flux = Heat transfer rate/Area

The Attempt at a Solution


The problem is that these are all the values I was given. I wasn't given any dimensions for the wall other than the thickness so I can't Calculate the area. Is this a mistake in the question or am I supposed to do it another way?
I attempted a solution by filling in all the values given in the relevant places but had to stop when I got to the area.

Thanks
 
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  • #2
Physicsswag said:

Homework Statement



I was given this question.

The wall of a building is constructed of face brick (10cm thick) and concrete block (50 cm thick) with an air filled cavity (5cm thick). The interior and exterior convection coefficients are 8.3 W.m^-2.K^_1 and 35W.m^-2.K^_1 respectively. The brick thermal conductivity is 0.79W.m^-1.K^_1 , the concrete block 1.63W.m^-1.K^_1, and the air cavity 0.26W.m^-1.K^_1. If the ambient air temperature is -10 degrees celsius and the room air temperature is 21 degrees Celsius, what will be the Heat flux through the wall.

Homework Equations


I know that Rtotal is equal to 1/h-inA + L1/k1A + ... + Ln/knA + 1/h-outA (h= Heat transfer coefficient, k= thermal conductivity, L=length, A=area)

Heat transfer rate = (t1-t2)/Rtotal

Heat flux = Heat transfer rate/Area

The Attempt at a Solution


The problem is that these are all the values I was given. I wasn't given any dimensions for the wall other than the thickness so I can't Calculate the area. Is this a mistake in the question or am I supposed to do it another way?
I attempted a solution by filling in all the values given in the relevant places but had to stop when I got to the area.

Thanks
Why don't you work the problem assuming a unit area for the wall (say 1 m2).
 
  • #3
The Heat Flux is defined as the heat flow per unit area.

Chet
 

1. What is heat flux through a wall?

Heat flux through a wall refers to the rate of heat transfer per unit area through a given wall. It is a measure of the amount of heat that is transferred from one side of the wall to the other over a specific period of time.

2. How is heat flux through a wall calculated?

The heat flux through a wall can be calculated using the formula Q = kA(ΔT/Δx), where Q is the heat flux, k is the thermal conductivity of the wall material, A is the area of the wall, ΔT is the temperature difference between the two sides of the wall, and Δx is the thickness of the wall.

3. What factors affect heat flux through a wall?

The factors that affect heat flux through a wall include the thermal conductivity of the wall material, the temperature difference between the two sides of the wall, the thickness of the wall, and the presence of any insulating materials or other barriers.

4. Why is heat flux through a wall important?

Heat flux through a wall is important because it can impact the energy efficiency of a building or structure. A higher heat flux means more heat is being transferred through the wall, which can lead to higher energy costs for heating or cooling. Understanding and controlling heat flux can help improve energy efficiency and reduce costs.

5. How can heat flux through a wall be reduced?

There are several ways to reduce heat flux through a wall, such as using insulating materials, increasing the thickness of the wall, or adding barriers such as reflective coatings. Additionally, proper sealing of any gaps or cracks in the wall can also help reduce heat transfer. Ultimately, the most effective way to reduce heat flux is to choose materials with lower thermal conductivity and to ensure the wall is well-insulated.

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